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Life Cycles of Stars (Grades 9-12) - Page 11

Now let us look at things from a different angle. What if you knew that a certain supernova is located about 3 kiloparsecs from Earth. When astronomers look at the remnant with their telescopes, they measure it to be 8 arc minutes (480 arc seconds) in diameter. What is the radius of the remnant in kilometers? Scientists have also measured the expansion velocity to be 4,800 km/sec. In what year did the supernova occur? Perhaps you can look up in a library, or on the World Wide Web, information about supernovae observed to occur in that year and find the common name of this supernova remnant. Need a hint?... Johannes Kepler was a famous astronomer.

A Teaspoon of Starstuff

Subrahmanyan Chandrasekhar (1910-1995) was born in Lahore, a part of India that is now in Pakistan. He won a Government of India scholarship and entered Cambridge University in England to work on his doctorate. As he sailed from India to England, he thought a lot about the death of stars. Using Einstein´┐Żs theory of relativity, he calculated that stars of a certain mass should not become white dwarfs when they died; he believed that they should keep on collapsing. He put aside this work, earned his doctorate in 1934, and only later actively returned to his theory. He calculated that stars with more than 1.44 times the mass of the Sun (now known as the Chandrasekhar limit) would not become white dwarfs, but would be crushed by their own gravity into either a neutron star or a black hole. His work was viciously criticized by Sir Arthur Eddington, then the leading authority on stellar evolution and someone greatly admired by Chandrasekhar. His standing diminished by Eddington's attacks, he came to the United States and was hired to teach at the University of Chicago. There he continued his research, which produced significant advances in the field of energy transfer in stellar atmospheres. Eventually, his calculations about white dwarfs were proven correct. With the recognition of the Chandrasekhar limit, the theoretical foundation for understanding the lives of stars was complete. He won the Nobel Prize in physics in 1983.

There are indeed distinct differences in the states of matter contained in main sequence stars, white dwarfs, and neutron stars. The following exercise will help you to understand just how different they are!

Look at the following chart and use the information you find there to calculate how much a teaspoonful of each object would weigh here on Earth. Assume that a teaspoon will hold about 5 cubic-centimeters of material.

ObjectMass (grams)Radius (cm)
Sun2 x 10 337 x 1010
White Dwarf1 x 10 335 x 108
Neutron Star2 x 10 339 x 10 5

Can you now relate these numbers to materials you know here on Earth? How much does a teaspoon of water weigh? Or air? Or iron?

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A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC

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